Secondary Injection 99 S500 204K
 

I have researched most of the treads on this subject and posted many myself. Yet I have not yet found the source of my problem. I have tried different things to see if it made a difference. The last thing I have done seems to work but does not fix the problem. Maybe it will point to the problem for those in the know. When my auto has set overnite I can drive a few minutes down to the stop lite. If I have to set a moment or so it starts to stutter on again off again until the CEL comes on then when warm smooths out and runs fine the rest of the day. If I make the lite and hit the interstate the lite stays off and I can drive with no problem. I have found that if I turn the engine off when I first get to the lite and start it back up I have no stutter and no lite. Does anyone have a clue!! This has been going on for 60K miles or so.

Have you had codes read from the system?

Is the car a W140 with M119 engine?

Yes & yes code was po410

P0 410 code means that either or both of the front O2 sensors aren't seeing enough oxygen when the air pump is activated.

WHY is the question. Does the scanner that diagnosed that code have the capability of activating that system & then showing the results of the front O2 sensors?

Both were replaced. The scanner showed left front below normal range, right front showed weak. I replaced LF about 25K miles ago, RF last week, I have not run O2 stats since changing . Should I check for EGR blockage? If so where and how? Also I read that I may need to reset ECU since replacing O2 sensors. Is this required to get smoother engine and max gas mileage?

Almost NEVER a bad O2 sensor! most of the time there is blockage in the system OR the pump doesn't run.

Performing an activation is the only good way to diagnosis.

OK so where would I start to look for blockages?

I can hear the pump running

Checked MOT and pulsating fine

Where is EGR vlave located?

Car doesn't have an EGR valve, you are getting bad info somewhere.

The only items involved in air injection are; air pump, air pump relay, hoses, diverter valve, switch-over valve, & ports inside the cylinder heads. The O2 sensors are the monitors for the system.

Why not test & stop guessing? An activation test takes about 10-20 minutes & can diagnosis the problem in less than an hour.

Thanks MB for the quick responses and info. You have been very helpful. The last activation I did was last Oct ($90) and the O2 information came from it. I was also told that there could be possibly carbon build up in the ports and that this has been cleaned by diyers but I never found out the proceedure. Last week I had codes ran because of a slight miss while driving in traffic no noticed as much when on the highway. The O2 showed not reading. I have never replaced the right front but had replaced the left front as I meantioned earlier. I replaced the FR O2 and reset the ECU according to procedure found on forum and the problem went away. I still have the CEL with PO410 code in the mornings only after setting overnite. I have had the full code and activation run twice in the last 2 years ($90 & $75 respectfully)with no reasonable explaination. Please do not get me wrong I do not mind paying for results I am just unable to pay out with shrugged shoulders be the result. I appreciate your help as always and I continue learning more and more which has helped more than you know. Best Regards MBD

Doc,Could a sporadic MOT cause a stumbling cold idle? I have checked the pulse of the MOT. It will start pulsating when I first crank the auto cold After a few minutes it shuts down and does not come back on. When the fan comes on I hear a click from inside the auto from the left side of the steering wheel dash area. Right after the click the auto starts stumbling and triggers the CEL. Once the auto is warm and O2 sensor activated I can reset the CEL and drive all day without a CEL. I found this out yesterday when checking for the MOT pulse after warmup. I removed the MOT and cleaned it out with carb cleaner and contact cleaner then let it set upside down filled with WD40 in both sides. I tapped the WD40 out and reconnected the MOT to the wired plug and started the engine. I then plugged the pulling side vaccuum and the MOT started pulsating and ticking as described in another tread. I then plugged in the other side. After several minutes as the engine began to warm the pulsating stopped and started between the fan starting up. Once the engine was warm The pulsating stayed constant. Is it possible this was/is my source of the problem. I have know light yet but will have to wait till tomorrow to start again on a cold engine.